1905] TRUE & OGLEVEE—TOXIC ACTION OF POISONS 1g 
depressant phase of concentration. The doubling of the amount 
of sand brings the growth rate nearly to the normal rate of the control, 
a slight depressant action still being seen. The roots, however, 
survive in good condition, so far as their appearance indicates. The 
increase of the sand to 120%™ results in so advanced a degree of 
adsorption that the growth raie is thrown clearly into the acceleration 
stage, perhaps near the maximum. Further additions still further 
reduce the molecules in the free solution and show a stage of dilution 
Check growth rate 
Growth rate: mm. per 24 hrs. 
m/35000 + m//35000 m/35000 =m/35000 + M/35000 m/ 35000 
CuSO, CuSO, CuSO, CuSO, CuSO, CuSO, 
- - - ~ + 
408™ sand 80g™ sand 1208™ sand 1608™sand 2008™ sand 
FIG, 2. 
corresponding to the descending stimulus phase. The addition of 
200%™ of sand shows this reduction of the copper effect at its limit. 
The free solution is, physiologically, distilled water, so far as the 
duration of the experiment allows one to judge. Here then the 
progressive addition of quantities of a solid produces results paralleling 
the progressive dilution of the toxic medium, the underlying cause of 
these results being the gradual removal of molecules or ions from the 
free solution by the insoluble body present. 
In view of the evidence here presented and discussed, it is likely 
that the process recognized as adsorption plays an important réle in 
many problems of plant and probably of animal physiology. Experi- 
ments by the water culture method cannot be used as a safe basis for 
argument concerning soil conditions. The so-called absorptive 
